This page opens with a married couple filing jointly, $180,000 of MAGI before any conversion and a planned $50,000 Roth conversion. Together that is $230,000, which puts both spouses in tier 1 because the joint standard bracket ends at $218,000. How much more income fits? shows the other way to read it: $38,000 of conversion keeps the couple at the standard premium.
How to use it for a conversion
- Enter the AGI you expect without the conversion, and any tax-exempt interest. For a future year, this is an estimate: pensions, Social Security that is taxable, dividends, required withdrawals.
- Put the conversion in Extra income to test. The tier, the premiums and the cliff line now include it.
- Read the room table. Each row is the most you could add and still be in that bracket, measured from your income without the conversion, with that bracket’s surcharge for a year.
The two-year lag and unknown brackets
Income in 2026 sets 2028 premiums, and CMS only publishes the 2028 brackets in late 2027. The calculator’s newest figures are for 2027 premiums (provisional until CMS publishes them in November). The edges moved up from 2025 to 2026, but how far they move next is not known in advance, so an amount just under an edge today may not be under it in 2028.
Spreading a conversion
Because IRMAA is decided one year at a time, a large conversion done in one year can cost a high tier once, while the same amount spread over several years may stay in a lower tier each year, or under the first edge entirely. The room table gives the yearly size that fits; the tax side of the decision is beyond this calculator.
Conversions on $180,000 of joint MAGI
Both spouses on Medicare with drug coverage, 2027 brackets (provisional). The surcharge is for the two of you, for the one premium year the conversion affects.
| Conversion | MAGI with it | Tier | Surcharge a year, both |
|---|---|---|---|
| None | $180,000 | Standard | None |
| $10,000 | $190,000 | Standard | None |
| $25,000 | $205,000 | Standard | None |
| $38,000 | $218,000 | Standard | None |
| $38,001 | $218,001 | Tier 1 | $2,296.80 |
| $50,000 | $230,000 | Tier 1 | $2,296.80 |
| $100,000 | $280,000 | Tier 2 | $5,769.60 |
| $150,000 | $330,000 | Tier 2 | $5,769.60 |
| $250,000 | $430,000 | Tier 4 | $12,710.40 |
Worked out with the calculator's engine. Provisional: CMS hadn't published 2027 figures as of October 18, 2026, so these are the official 2026 figures. Sources: CMS, 2026 Medicare Parts A & B Premiums and Deductibles; SSA, Premiums: Rules for Higher-Income Beneficiaries; SSA, Request to lower IRMAA (the life-changing events).